Spark generating system



Aug. 15, 1939 L... ascent 18 SPARK GENERATING SYSTEM Filed Feb. 5, 1937 3 Sheets-Sheet 1 Aug. 15, 1939 L. H. scoT'f SPARK GENERATING SYSTEM 3 Sheets-Sheet 2 Filed Feb. 5, 193'! I e y "if"- Aug. 15, 1939 L. H. scoTT 2,169,818

SPARK GENERATING SYSTEM Filed Feb. 5, 1937 3 Sheets-Sheet 3 Patented Aug. 15, 1939 UNITED STATES PATENT OFFICE SPARK GENERATING SYSTEM Lloyd H. Scott, Sidney, N. Y.

Application February 3, 1937, Serial No. 123,885

9 Claims. (01. 123-148) The present invention relates to a spark generating system and more particularly to a system for generating electrical impulses of high voltage suitable for the ignition of internal combustion engines.

The development of high speed multi-cylinder engines has required the provision of ignition systems capable of producing and accurately timing adequate spark discharges at higher and higher frequencies until the usual forms of mechanically operated ignition apparatus are required to be operated at or above their maximum eflicient operating speeds. Thus a l4-cylinder engine rotating at 3,000 revolutions per minute requires 21,000 sparks per minute, and a 16-cylinder engine at 3500 revolutions per minute requires 28,000 sparks per minute, and in the immediate future still higher speed requirements will have to be met.

It is difllcult to design a mechanically operated ignition system which will deliver accurately timed efficient sparks at such speeds, and mechanical breakers do not have satisfactory endurance characteristics when so operated, due among other things to the heavy current which must flow in order to transmit suflicient energy forthe spark in the short time intervals involved. Moreover, in the conventional types of ignition apparatus in which the primary winding of an induction coil is energized by a heavy flow of current, the interruption of which causes the high tension discharge, the efliciency and life of the coil are limited by the heating effect of the currents flowing therein. Since such coils must be well insulated electrically, it is difficult for the heat to escape, and the temperature within the coil may during long periods of use rise sufliciently to cause deterioration or even disintegration of the insulating material.

It is also desirable from engineering, operative and service standpoints that the ignition current generating device be taken off the engine and thus freed from the vibration, heat and fouling thereof, and placed where it is readily accessible for inspection and adjustment; whereas this is impractical with the usual types of high speed ignition devices.

It is an object of the present invention to provide a novel high-speed ignition system for internal combustion engines which is efficient, reliable and inexpensive to manufacture and which is capable of efficient operation at speeds in excess of the maximum now commercially available.

It is another object to provide such a device in which the high tension discharge is caused by the building up of flux in an induction coil due to the sudden application of a comparatively high voltage to the primary thereof, in conchanical parts and therefore is not limited in speed by the inertia or elasticity of such parts.

It is another object to provide such a device which does not rely for the generation of high tension current on the collapse of electrically produced magnetic fields and therefore is free from the limits inherent in such systems.

It is another object to provide such a device in which the flow of primary current is controlled by means of electronic and photoelectric tube relays actuated by control currents of very small amperage.

It is another object to provide such a device in which the voltage requisite for the operation of the electronic and photoelectric tubes are all derived from a single power supply.

Another object is to provide such a device which may be arranged to supply an accurately regulable succession of sparks at each ignition point.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawings in which:

Fig. l is a diagrammatic representation of one preferred ignition system embodying the present invention;

Fig. 1a is a fragmentary detail of an optical arrangement of the circuit illustrated in Fig. 1;

Fig. 2 is a similar representation of a. second embodiment of the invention;

Fig. 3 is a vertical substantially mid-sectional view of a preferred form of timing device applicable to either of the specific systems illustrated; and

Fig. 4 is a detail in side elevation of a portion of a. typical form of aviation engine showing applicants novel timing device incorporated therewith.

Referring first to Fig. 1 of the drawings, a

source of direct current at high voltage indicated generally by numeral is illustrated in the form of a conventional type of power pack including a transformer 2, having a primary 3 energized by a suitable source of alternating current 4, low voltage secondaries 5 and 6 used for filament or heater supply, and a .high voltage secondary 1 having a center tap grounded as indicated at 8 and the two ends connected to the plates 9 and H of a full-wave power rectifier tube |2 such as the type designated commercially by the number 82. 7 The cathode-filament l3 of tube I2 is heated from the low voltage secondary 6 of the power transformer 2 and lis connected by a lead M to a suitable choke 15, the ends of which are grounded through condensers l6 and IS in the conventional manner inorder to smooth out the alternating current ripple and supply comparatively pure current. The output from the choke I5 is c mnected by a lead H to a voltage divider com "rising four resistances l8, I9, 20 and 2| in ries, the free end of resistor 2| being grounded in order to complete the return circuit through the center tap 8 of the transfonnersecoridary 1.

According to the present invention, a gridcontrolled gas-filled discharge-tube 22 is utilized to intermittently apply {the voltage from the power pack I to the priinary 23 of an output transformer 24, theseoondary 25 of which is connected by a lead 26 to an ignition device indicated diagrammatically at 21. For this purpose, the filament 38 tube 22 is heated from the secondary winding 5 of the power transformer, the plate 28 is connected by lead 29 to the low voltage end of resistor l8 whereby said plate is connected to the power pack through the resistor I8; the cathode 3| is connected by lead 32 to the primary 23 of output transformer 24,

and the opposite end' of said primary is connected through lead 33 and resistor 2| to the ground. A condenser 34 is connected between the plate lead 29 and cathode lead 33'whereby said condenser is charged by virtue of the voltage drop across resistors l9 and 20 when tube 22 is in its non-conductive state, and discharges through the tube when the tubeis rendered conductive.

In order to control the operation of tube 22, its grid 35 is grounded through a suitable resistance 36 whereby when no current is flowing through resistance 36, the grid is at ground potential and accordingly has a negative bias with respect to the cathode 3| by virtue of the voltage drop across the resistor 2|. This negative grid bias renders the tube non-conductive. Means for intermittently imparting to the grid 35 a positive bias with respect to the cathode 3| in order to render tube 22 conductive is provided comprising a photoelectric cell 31, the cathode 38 of which is connected by a lead 39 to the said grid, and the anode 4| of which is connected by a lead 42 to a tap 43 in the voltage divider at the high voltage end of resistor 20. It will be seen that by this arrangement when the, photoelectric cell 31 is rendered conductive, a current will flow from the tap 43 of the voltage divider through lead 42, photoelectric cell 31 and lead 39 through resistor 36 to the ground whereby the grid 35 will be rendered positive with respect to the ground by virtue of the voltage drop through the resistor 36 caused by the flow of current therethrough.

source indicated generally by numeral 44 arranged by means of any suitable form of reflecting and condensing system such as indicated at 45 and 45 to throw a beam of light having'a focus at 41 and so directed as to illuminate the cathode 38 of the photoelectric cell 31. At or near the focal point 41 of the light beam, an obturating apparatus is provided, a fragment of which is here shown in the form of an opaque disc 48 provided with suitable openings 49 and arranged to be rotated in timed relation with the engine to be ignited, such that the openings 49 permit the passage of the light beam only at such times as an ignition discharge at the ignition device 21 is desired.

In the operation of this embodiment of the inyention, the power pack and the light source 44 being suitably energized, rotation of the disc 48 by the engine causes the beam of light from said source to intermittently fall upon the cathode 38 of the photoelectric tube 31 and thereby render said tube conductive. The grid 35 of tube 22 is thereby rendered positive with respect to the cathode 3| thereof whereby tube 22 becomes'conductive and an impulse of current'stored in condenser 34 is caused to flow through the primary 9 23 of output transformer 24, causinga high tension discharge from the secondary 25 thereof to take place at the ignition device 21. When the condenser 34 has become discharged to such an extent that the voltage impressed on tube 22 is below that necessary to sustain the discharge therethrough, the tube heals, and since the grid 35 thereof has resumed its negative bias as a consequence of the light beam being interrupted by rotation of the disc 48 moving the opening 49 out of range of said beam, the condenser 34 will be recharged by current flowing through the resistor I8. Resistor I8 is, of course, of such value as to so limit the current therethrough that'it will not maintain a continuous discharge through the tube 22. If a series of sparks are desired at each ignition point of the engine, this, of course, may readily be obtained by suitably proportioning the capacity of the condenser 34, resistor l8 and openings 49 in disc 48 so that condenser 34 may charge and discharge through tube 22 any desired number of times while an opening 49 in the disc is in the path of the light beam.

Inasmuch as it is the building up of the flux through the primary 23 of the output transformer 24 which is depended upon to produce the secondary discharge, and the maximum current flow through said primary is of extremely short duration, it is obvious that the voltage which may safely be applied thereto without overheating is many times what would be permissible in a conventional ignition system in which the flux'must obtain its maximum value for an appreciable time and then be interrupted so as to cause a. collapse of the field occasioned thereby in order to gengas-filled grid-controlled tubes may readily be'obtained of practically any desired current-carrying capacity, it is obvious that there is here provided a system by which any desired amount of energy may be supplied to an ignition device under accurate timing control at speeds far beyond any present or anticipated requirements. The operation of charging the condenser 34 may be considerably expedited by connecting said condenser to the output of the power pack I through a suitable inductance instead of the non-inductive resistor ll. Fig. la. shows such an arrangement inwhich an inductance 5| con-' nects the plate lead 29 of tube 22 to the output lead I! of the power pack I.

When such an inductance is used, the fiow of current therethrough during the discharge through tube 22 causes a field to be built up around the inductance, and when the tube heals, the consequent reduction in current fiow through the inductance causes a collapse of this field which augments the flow. of charging current into condenser 34. It has been found in the operation of this arrangement utilizing a suitable choke coil as an inductance that sparks may be generated at'such high speeds as to produce pure musical tones.

In the form of the invention illustrated in Fig. 2, continuous electrical oscillations are generated by means of a conventional type of oscillating circuit, which oscillations are built up by means of a suitable amplifier to energize an output transformer for producing the ignition sparks. The control of the output is preferably effected by means of a photoelectric device for rendering the amplifier operative or inoperative. As here shown, the oscillating circuit comprises an ordinary grid-controlled triode 52 comprising a cathode 53, a grid 54 connected to a tank circuit 55 through a grid leak 56 and condenser 51, and a plate 58 connected to a direct current voltage supply through 'a lead 58 and provided with a tickler coil 6| in inductive relation with the tank circuit 55, the coupling of the tickler being such as to maintain the tube 52 in an oscillating condition. The oscillator tube 52 is resistance-coupled to an amplifying tube 52 by means of a suitable resistor 63 in the plate circuit of tube 52 and a coupling condenser 64 connected to the grid 55 of the amplifier, the grid 65 being grounded through a suitable grid leak 66, and the cathode to being grounded through a resistor bridged by a condenser 60".

A stage of transformer-coupled push-pull amplification is interposed between the amplifier tube 62 and an output transformer 61, this amplifying stage comprising two tubes SI and IS, the grids of which are connected to the opposite ends of the center-tapped secondary of an input transformer H, the primary of which is inserted in the plate lead 10 of tube 82, while the plates of said tubes are connected to the opposite ends of the center-tapped primary of the output transformer 61, all in the usual and well-known manner. The output of transformer 61 is arranged to actuate a suitable ignition device for the engine to be ignited illustrated diagrammatically at 13.

The timing of the discharges from this generating system is accomplished by means of a photoelectric valve which places a paralyzing voltage on the grid 55 of amplifier tube G2 when the photoelectric tube is rendered conductive. As here shown, this arrangement comprises a biasing battery 14, the negative pole of which is connected to the cathode I5 of a photoelectric tube 16, the anode 11 of which is connected by a lead 18 to the grid 65 of tube 62. A disc 19 rotating in timed relation with the engine to be ignited is placed in the path of a beam of light produced by a light source 8i, said disc being provided with openings 82 permitting said light beam to pass at all times except when an ignition discharge is desired.

'In the operation of this form of the invention, the tube 62 being in a state of oscillation at a frequency well above the highest natural spark frequency desired as determined by the constants of its oscillating circuit, and disc 19 being so positioned as to interrupt the light beam, the normal plate current through the amplifier tube 62 and resistor 60' places only suflicient bias on the grid 55 for its normal operation as an amplifier. The oscillations generated by tube 52 are accordingly amplified by tube 62 and again amplified by tubes 68 and 69 and transmitted to the output transformer 61 to produce a train of sparks at the ignition device 13. When the disc 19 is rotated so as to bring an opening 82 in the path of the light beam, photoelectric tube 15 is thereby rendered conductive whereby the battery I4 is caused to negatively bias the grid 65 of tube 52 so as to paralyzejsaid tube and thus interrupt the spark discharge.

Inasmuch as the tube 52 is in a continuous state of oscillation so that it is unnecessary to build up oscillations for each discharge desired, and the control of the grid circuit of the amplifying tube is substantially instantaneous, it is clear that this system also is capable of generating high tension discharges at practically any desired rate and with accurate timing control.

One form of timing and distributing mechanism for use in conjunction with either of the above spark-generating systems is illustrated in Fig. 3. As here shown, a casing 83 is provided suitably formed for mounting on a convenient part of the engine to be ignited and having suitably journalled therein a shaft 84 adapted to be rotated in timed relation with a rotating part of the engine. A light source 85 of any suitable type is mounted on the casing and provided with a reflector 86 arranged to focus 'a beam of light approximately at an opening 81' in a housing 88 which encloses a photoelectric tube 89. If desired,

a condensing lens 9| may be incorporated in the system to concentrate the beam upon the cathode screen 92 of the photoelectric tube.

An obturator in the form ofa drum 92 is mounted on the rotary timer shaft 84 and is provided with openings 84 in the path of the beam of light from the source 85,v the arrangement being such that when the openings 84 in the obturator register with the opening 81 in the cell housing, the photoelectric tube will be rendered conductive by the incidence of the light beam thereon. Vanes may be mounted on the obturator 93 to assist in dissipating the heat from the light source.

Timer shaft 84 may also be used to operate a distributor for connecting the ignition devices of the different engine cylinders to the high tension output in proper sequence. this is accomplished by mounting a distributor block 95 on the casing 83 by means of a cap 96, a central terminal 91 in said block being con- As here shown,'

nected to the high tension output, and a plurality of circularly arranged terminals 98 being connected by cables 89 to the ignition devices" of the engine. A distributor rotor i0! is mounted on the upper end of shaft 84 and carries a con ductor I02 for connecting the central electrode 51 to the electrodes 58 in sequence. It will be understood that this distributing arrangement here shown, this is accomplished by a flange mounting of the casing 83 on a suitable extension of the engine casing serving to house a suitable form of drive for actuating timer shaft 84.

It will be understood that the photoelectric tube 89 may be connected to operate either in the manner of the photoelectric tube 31 of Fig. 1 or the photoelectric tube 16 of Fig. 2, and the obturator 93 will be correspondingly formed so as to have the openings 94 arranged to register with the opening 81 of the casing at the ignition points when the circuit of Fig. l is employed, or to be out of registry therewith at such times when the circuit of Fig. 2 is employed.

Although certain examples and preferred forms of the present invention have been illustrated and described in detail, it will be understood that other embodiments are possible and that various changes may be made in the arrangements and design of the parts without departing from the spirit of the invention as defined in the claims appended hereto.

What is claimed is:

1. In an ignition system for internal combustion engines, a primary circuit including a power source, a three-element gas-filled electronic tube and the primary winding of an induction coil, means normally maintaining the control element of said tube suiliciently negative with respect to the cathode to render the tube non-conductive, means for periodically raising the voltage of the control element sufliciently to render the tube conductive, and means forso limiting the flow of current from said power source as to allow the tube to heal after each discharge therethrough.

2. In an ignition system for internal combustion engines, a primary circuit including a power supply, a thyratron including a cathode, anode, and control grid, and the primary of a transformer, a voltage divider connected across the power supply including a resistor in series with the primary circuit, a resistor connecting the grid to the negative side of the power supply, the cathode return being tapped into the voltage divider spaced from the negative end thereof to bias the cathode positively relative to the grid, a grid control circuit tapped into the voltage divider above the cathode return, and means'for closing and opening the grid circuit in synchronism with the operation of the engine to be ignited. 3. In an ignition system for internal combustion engines, a primary circuit including a. power supply, a thyratron including a cathode, anode, and control grid, and the primary of a transformer, a voltage divider connected across the power supply including a resistor in series with the primary circuit, a resistor connecting the grid to the negative side of the power supply, the cathode return being tapped into the voltage divider spaced from the negative end thereof to bias the cathode positively relative to the grid, a condenser connected to discharge through the thyratron and the primary of said transformer, a grid control circuit tapped into the voltage divider above the cathode return including means synchronized with the engine to be ignited for intermittently imparting a positive bias to said control grid.

4. In an ignition system for internal combustion engines, a source of high frequency electrical oscillations, an amplifying system therefor including an electronic tube having a control grid on which said oscillations are imposed, and means synchronized with the engine to be ignited for intermittently applying a cut-off bias to said grid.

5. In an ignition system for internal combustion engines, an undampedoscillator, an amplii'ying system therefor including an input thermionic tube having a grid upon which said oscillations are impressed, means normally maintaining said grid at a potential to render the tube effective as an amplifier, a control circuit for said grid including a source of voltage sufiicient to block the tube, and means synchronized with the engine to be ignited for closing and opening said control circuit. 7

6. In an ignition system for an internal combustion engine, a source of elecrical energy, an output transformer, means including an electronic tube for conducting impulses of electrical energy from said source to the primary ofsaid transformer, and means for timing said impulses in accordance with the operation of the engine including a photoelectric cell separate from the source and connected with the grid of said tube for controlling the flow of said energy therethrough from said source to said transformer, a source of light impinging on said photo-electric cell for energizing the same and means operated in timed relation with said engine for intermittently interrupting said light.

7. In an ignition system for an internal combustion engine, a source of electrical energy, an output transformer, means including an electronic tube for conducting electrical energy-from said source to the primary of said transformer, and means forintermittently interrupting the flow of said energy from said source to said transformer-including a photo-electric cell separate from said source and connected with said tube for controlling the flow of said energy therethrough, a source of light impinging on said photo-electric cell for energizing the same and means operated in timed relation with said engine for intermittently interrupting said light.

8. In an ignition system for internal combustion engines, a primary circuit including a source of electrical energy, an electronic tube having a control grid and the primary winding of an induction coil, and means for controlling theflow of current from said source to said winding through said tube to cause said flow to be intermittent, said means including a photo-electric cell separate from said source and connected with said control grid and means for intermittently energizing said photo-electric cell in accordance with the operation of the engine.

9. In an ignition system for an internal combustion engine, a primary circuit including a source of electrical energy, a gaseous discharge tube and the primary winding of an induction coil, and means outside said circuit for intermittently interrupting the flow of electrical energy from said source to said transformer including a photo-electric cell connected with said tube and means for intermittently energizing said cell in accordance with the operation of the engine.

LLOYD H. SCOTT. 

